1. Field of the Invention
The present invention relates to a seat slide device for an automotive seat, which is adapted to adjust the forward and backward positions of the seat, and more particularly relates to an improvement on a seat slide device comprising upper and lower rails, the upper rail being slidably fitted to the lower one, in which a seat belt is at its one end anchored to the upper rail or a seat frame of the seat, in order that the upper rail is prevented from its removal out of the lower rail.
2. Description of the Prior Art
Most of generally designed seat slide devices are essentially composed of a lower rail to be fixed to the floor of an automobile and an upper rail to be fixed to the bottom surface of a seat, with such an arrangement that the upper rail is fitted to the lower rail in a slidable fashion. In actual use, a pair of thus-constructed slide devices are each provided on the respective lateral sides of a seat.
Referring to FIG. 1 of the accompanying drawings, illustrated is an example of conventional seat slide device of this kind. In this particular device, a roller (50) is disposed between a lower rail (112) and an upper rail (114), and a steel ball (122) is embraced by both inwardly bent end (128) of the upper rail (114) and outwardly bend end (124) of the lower rail (112). It is, then, understandable that a vertical force is exerted on the roller (50) whereas vertical and transverse forces are exerted on the steel ball 122).
The advantage of such prior, therefore, is found in no possibility of the upper rail (114) being dislocated vertically or laterally relative to the lower rail (112), allowing the former rail to smoothly slide along the latter rail.
Although not shown in the drawings, a locking structure is in most cases arranged in the foregoing seat slide device, such that a plurality of equidistant projected pieces are formed on the upper rail (114) and a plurality of lock apertures are formed in the lower rail (112) in correspondece with the respective projected pieces, whereby the upper rail (114) can be locked at a desired position on the lower rail (112) when the projected pieces are brought to engagement into the respective lock apertures.
In the above-mentioned device per se, there is no problem in the case of a sudden accident like a collision taking place, with a great load applied thereto. This is particularly the case when a seat belt is not attached around the body of an occupant on the seat. The reason is that, in such accident, the upper and lower rails (114)(112) are given a maximum load only when the occupant is forced backwards to hit his body to the seat back of his seat provided on those rails, at which time, due to such load upon the seat back, an upward pulling force is exerted on the forward point where the forward end portion of the seat is connected to the corresponding portion of the upper rail (114) while at the same time a downward pressing force is exerted on the rearward point where the rearward end portion of the seat is connected to the corresponding portion of the upper rail (114), but the former pulling force (designated by "F" in FIGS. 1 and 2), although tending to remove away the forward end portion of the upper rail (114) from the lower rail (112) in an arrow direction as in FIG. 1, is not so sufficiently great as to remove the upper rail (114). Therefore, the seat slide device is not damaged in such case.
However, in view of the recent circumstances where attaching a seat belt is a mandatory legal requirement for drivers who sit on automotive seats, it is true that every automobile has seat belts mounted therein, and when it is desired to secure one end of the seat belt to the seat frame of the seat or the upper rail of the seat slide device, the aforementioned type of conventional seat slide device is not rigid enough to resist such upward pulling force caused by a collision accident or the like.
In other words, when a seat belt is fixed to the upper rail (114) or the seat frame disposed thereon, in case of a collision accident occuring, the seat belt, which restrains an occupant to the seat, is pulled by the forward inertia force of the occupant, transmitting a maximum pulling force to the seat slide device. In this case, a downward pressing force is exerted on the above-discussed forward point (a point where the forward end portion of the seat is connected with the upper rail (114)), and an upward pulling force is exerted on the above-discussed rearward point (a point where the rearward end portion of the seat is connected with the upper rail (114)). The latter upward pulling force is far greater than the above-mentioned upward pulling force which is caused in the case of nonattaching the seat belt, as a result of which, as shown in FIG. 2, the upper rail (114) is forcibly moved upwards, with the inwardly and outwardly bent ends (128) (129) of the lower rail (112) being deformed, increasing the possibility of the upper rail (114) being removed out of the lower rail (112). If the upper rail (114) is removed from the lower one (112), it will be inevitable that the occupant will be thrown out forwardly together with the seat into a terrible fatality.
To solve this problem, there are some conventional devices having a great cross-section of upper rail and lower rail, or the upper and lower rails of thick steel plate to reinforce its rigidity in order to avoid deformation of those rails as well as removal of the upper rail. But, these proposals have been found defective in that such great cross section results in unfavorably big dimensions of the device as it takes up a large space, and further increased weight thereof, and such thick rails also lead to the same result.